Sidescan sonar is an acoustic imaging technology that uses high frequency (100 kHz to 2.4 MHz and higher) sound waves to “illuminate” the sea floor and produce realistic pictures of what lies at the sediment-water interface, and in the water column. As sound waves propagate away from the sidescan transducers, objects in the path of the beam reflect some of the acoustic energy back to the transducer, and these signals are then amplified, processed, and passed on to a video display, printer or computer vision/processing algorithms.
The earliest imaging sonar research is credited to British and German researchers beginning in the 1920's and 1930's, but suffered from the limitations of analog technology, namely attenuation of the sonar signal as it traveled further along copper wires, and deficiencies with the primitive signal display and recording equipment available at the time. Today, advances in digital signal processing and increased computational power have largely overcome these problems. Modern high frequency systems can reliably image objects that are smaller than 1 cm3 and digital software can “stitch” together sonar records to make high-resolution, geo-referenced mosaics of the seafloor.
Side scan sonar proved its capabilities during the 1960's and 1970's as an indispensable tool to locate wreck, mines, lost nuclear weapons, and downed submarines and aircraft. The petroleum industry pioneered the commercial use of sidescan sonar for pipeline routing and inspection in the 1970's and 1980's as offshore drilling became popular. As the 1990's progressed, sidescan sonars became available in higher and higher frequencies that allowed significant advances in imaging resolution. With increased resolving power, common to modern systems, sidescan sonar has been used to map and classify marine fisheries habitats, detect and enumerate salmon during their upstream migrations, investigate trawl damage to marine habitat, and map relic oyster reefs in turbid, low visibility environments.
In view of the following an improved method and system is needed for identifying sonar targets within a liquid medium.